The new iTunes looks fantastic & has some great new features.
However any quick survey of forum discussions will show you that there are some bugs that people are discovering.

For me (imac G5 10.4.7) i installed it only to find that no songs would play!
its clearly a common problem which is easily fixed.

Its simply a matter of checking your plug ins… (~ / Library / iTunes / iTunes plug ins).
For me and lots of others the offending plug in was OSS 3D. But there could be others. Delete the plug in & iTunes 7 works great!